1. Field of the Invention
The present invention relates to a blood pump and, more particularly, to the blood pump which is compact and lightweight and easy to manufacture and which can be substantially safely operated for a substantially prolonged length of time without being substantially accompanied by hemolysis while exhibiting a favorable discharge efficiency.
The present invention also relates to an extracorporeal blood circulating apparatus utilizing the blood pump of the type referred to above.
2. Description of the Prior Art
It is well known that a blood pump is extensively used in an extracorporeal blood circulating circuit such as used with, for example, an artificial cardiopulmonary system or an assisted circulatory system for the cardiac function used subsequent to the cardiopulmonary operation. An attempt is now largely being made to use a centrifugal pump as the blood pump for use in the extracorporeal blood circulating circuit.
The centrifugal blood pump generally used in the extracorporeal blood circulating circuit is of a design comprising a pumping chamber communicated with an inflow port on one hand and with an outflow port on the other hand, and a rotary vane assembly accommodated within the pumping chamber for rotation in one direction. This extracorporeal blood pump of centrifugal type is operable to discharge the blood at a controlled rate determined according to the number of revolutions of the vane assembly and the difference between the pressure of the blood supplied to the inflow port of the extracorporeal blood pump and the pressure of the blood discharged from the outflow port of the extracorporeal blood pump, that is, a pressure differential across the extracorporeal blood pump.
The extracorporeal blood pump of the centrifugal type is recognized as being advantageous in that it requires the use of neither expensive artificial valves nor a synchronizing device, both necessitated in a extra corporeal blood pump of pulsating type and can therefore be manufactured compact and light weight at a substantially reduced cost. Also, unlike a peristaltic blood pump comprising a rotor having a plurality of radially outwardly extending arms, each having a roller mounted rotatably on a free end thereof, and operable to successively displace the blood flowing in a flexible tube as the rollers squeeze consecutive portions of the flexible tube during rotation of the rotor, the centrifugal extracorporeal blood pump is known having no problem associated with a fatigue-based failure of the flexible tube and can therefore withstand a prolonged time of use.
Some examples of the prior art centrifugal extracorporeal blood pumps are shown in FIGS. 1 and 2 of the accompanying drawings, respectively, in schematic longitudinal sectional representations, reference to which will now be made for the detailed discussion.
The centrifugal extracorporeal blood pump shown in FIG. 1 comprises a pump housing 16 defining a pump chamber therein and having a blood inflow port defined therein, and a rotary vane assembly rotatably supported within the pump chamber and including a generally disc-shaped pedestal 11 having a generally cylindrical peripheral surface and also having a flat base face at one end and a generally conical top end face opposite to the base face, and a plurality of vanes 12 rigidly mounted on a peripheral edge of the disc-shaped pedestal 11 adjacent the conical top end face so as to extend radially outwardly therefrom. The rotary vane assembly is drivingly coupled with a drive motor (not shown) having a drive shaft 14 connected to the disc-shaped pedestal 11 for rotation together therewith. This prior art centrifugal extracorporeal blood pump shown in FIG. 1 is operable in such a manner that, during the rotation of the rotary vane assembly in one direction driven by the drive motor, the blood entering the inflow port which is generally in alignment with an apex of the shape of the conical top end face of the pedestal 11 is drawn into the pump chamber so as to flow radially outwardly within the pump chamber as indicated by 13.
It has, however, been found that eddy currents, as indicated by 15, of the blood flowing within the pump chamber tend to occur in the vicinity of the outer perimeter of the pedestal 11, imposing relatively large stresses on blood corpuscles to an extent that the blood corpuscles may be destroyed, resulting in hemolysis.
On the other hand, another prior art centrifugal extracorporeal blood pump shown in FIG. 2 comprises a pump housing 19 defining a pump chamber therein and having a blood inflow port defined therein, and a rotary vane assembly rotatably supported within the pump chamber and including a generally disc-shaped pedestal 17 having a flat base face and a generally conical top face opposite to the base face, and a plurality of vanes 18 rigidly mounted on a peripheral portion of the disc-shaped pedestal 17, which is spaced a distance radially outwardly from an apex of the shape of the conical top face, so as to extend radially outwardly therefrom. The rotary vane assembly is drivingly coupled with a drive motor (not shown) having a drive shaft 20 connected to the disc-shaped pedestal 11 for rotation together therewith. This prior art centrifugal extracorporeal blood pump shown in FIG. 2 is operable in such a manner that, during the rotation of the rotary vane assembly in one direction driven by the drive motor, the blood entering the inflow port which is generally in alignment with an apex of the shape of the conical top face of the pedestal 17 is drawn into the pump chamber so as to flow radially outwardly within the pump chamber as indicated by 21.
Again, it has been found that the prior art centrifugal blood pump of the construction shown in FIG. 2 has the following problem. Namely, since the flat base face of the disc-shaped pedestal 17 has a surface area enough to cover the substantially entire bottom surface of the pump housing 19 which confronts the flat base face of the disc-shaped pedestal 17, no eddy current is induced in the flow of the blood being pumped such as occurring in the extracorporeal blood pump shown in and described with reference to FIG. 1. However, even the extracorporeal blood pump shown in FIG. 2 is not only more or less unable to minimize to a satisfactory or required level any possible occurrence of hemolysis, but also tends to exhibit an insufficient blood discharge efficiency.
Also, the extracorporeal blood pump shown in FIG. 2 employs the vanes 18 each being in the form of a curved plate when viewed from top of the pedestal 17, and therefore, it has been difficult to the vane assembly of a type in which the pedestal 17 is integrally formed with the vanes 18.
On the other hand, an extracorporeal blood circulatory device is often used during a medical treatment of a patient, for example, during a cardiac operation or a blood dialysis. The prior art extracorporeal blood circulatory device has the following problems because the drive shaft of the extracorporeal blood pump is coupled direct with the motor drive shaft.
(I) The extracorporeal blood circulatory device is generally required to be so compact and so lightweight that it can be installed bedside and close to a patient lying on a bed and is quiet enough to prevent the patient from being disturbed by noises. However, the prior art extracorporeal blood circulatory device is bulky and heavy in weight and is therefore inconvenient to transport from a storage room to the patient's bedside. Moreover, the drive motor and the movable component parts of the prior art extracorporeal blood circulatory device tend to emit offensive noises and, therefore, it has been recommended to avoid a bedside placement of the extracorporeal blood circulatory device.
Where the bedside setting of the extracorporeal blood circulatory device is inevitable, the extracorporeal blood circulatory device requires noise buffering plates or material to be fitted to the device, resulting in a necessity of the use of a casing of increased size enough to accomodate the noise buffering system. This in turn brings about an increase in size and weight of the extracorporeal blood circulatory system as a whole.
(II) It has often been observed that heat generated from the drive motor used in the extracorporeal blood pump tends to be transmitted from the drive shaft of the motor to the blood flowing within the pump chamber through the drive shaft of the extracorporeal blood pump. Once blood flowing within the pump chamber is heated, the blood is susceptible to hemolysis under the influence of the heat.